606
FXUS61 KBOX 192307
AFDBOX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BOSTON/NORTON MA
707 PM EDT SAT JUL 19 2025
SYNOPSIS
WARM AND HUMID ON SUNDAY WITH TWO ROUNDS OF THUNDERSTORMS
POSSIBLE. THE FIRST ROUND WILL BE IN THE MORNING NEAR THE SOUTH
COAST. THE SECOND ROUND WILL BE IN THE LATE AFTERNOON TO EVENING
WITH SEVERE WINDS POSSIBLE. MUCH LESS HUMID ALONG WITH COOLER
THAN NORMAL TEMPERATURES AND DRY WEATHER FOR MONDAY AND TUESDAY.
WARMING TREND THEN BEGINS WEDNESDAY, WITH HEAT AND HUMIDITY
RETURNING FOR THURSDAY AND ESPECIALLY FRIDAY WHEN HIGHS MAY
REACH WELL INTO THE 90S IN SOME LOCALES. THE MAIN RISK FOR SOME
SHOWERS AND THUNDERSTORMS EXISTS SOMETIME FRIDAY/FRIDAY NIGHT
WITH A PRE- FRONTAL TROUGH AND ASSOCIATED COLD FRONT.
NEAR TERM /THROUGH SUNDAY/
TONIGHT THROUGH SUNDAY MORNING
KEY POINTS
* INITIALLY DRY WITH INCREASING HUMIDITY OVERNIGHT
* ROUND OF HEAVY RAIN AND POSSIBLY ISOLATED FLASH FLOODING NEAR THE
SOUTH COAST AND ISLANDS BETWEEN 6-10AM.
INCREASING CLOUD COVER TONIGHT AHEAD OF A WEAK SHORTWAVE ALOFT AND
INCREASING SOUTHERLY FLOW. DEWPOINTS WILL RISE QUITE A BIT FROM THE
MID-50S THIS AFTERNOON TO THE UPPER 60S BY SUNDAY MORNING. THIS
WILL KEEP OVERNIGHT LOWS MUCH WARMER THAN LAST NIGHT IN THE MID TO
UPPER 60S. THE FORCING FROM THE SHORTWAVE ARRIVES EARLY SUNDAY
MORNING, ENHANCED BY A WEAK 20-30 KNOT LLJ. THE LLJ WILL HELP
QUICKLY INCREASE INSTABILITY (MUCAPE) VALUES OVER THE SOUTHERN
COASTAL WATERS IN THE CAPE AND ISLANDS, WHERE AS MUCH AS 1000 J/KG
COULD BE AVAILABLE BY 12Z. WITH PWATS NEAR 2 INCHES ALONG THE SOUTH
COAST, AND WARM CLOUD DEPTHS AROUND 12KFT, MORNING THUNDERSTORMS
WILL CONTAIN VERY HEAVY RAIN. THE LATEST 12Z GUIDANCE HAS SHIFTED
THE THUNDERSTORM ACTIVITY SLIGHTLY FURTHER SOUTH THAN THE 00Z
GUIDANCE, SO THE MOST LIKELY AREAS TO BE AFFECTED BY THUNDERSTORMS
WILL BE THE SOUTHERN COASTAL WATERS AND THE ISLANDS. WITH RATHER
SANDY SOILS ACROSS THE CAPE AND ISLANDS, QPF TOTALS WOULD NEED TO
EXCEED 4-6 INCHES IN 3 HOURS FOR FLASH FLOODING TO OCCUR. IF STORMS
WERE TO VENTURE FURTHER NORTH, INTO PROVIDENCE, FALL RIVER, OR NEW
BEDFORD, THEN FLASH FLOODING WOULD BECOME MORE LIKELY AS RAINFALL
TOTALS COULD EASILY EXCEED FLASH FLOOD GUIDANCE OF 2-3 INCHES IN 3
HOURS. GIVEN LOWER CONFIDENCE ON STORMS REACHING THOSE FLASH FLOOD
PRONE AREAS, HELD OFF ON A FLOOD WATCH AT THIS TIME. THE SEVERE
THREAT LOOKS LIMITED IN THE MORNING AS THE INSTABILITY REMAINS
ELEVATED; HOWEVER, THE NOCTURNAL INVERSION IS NOT TYPICALLY AS
STRONG OVER THE WATERS, AND SOME STRONGER WIND GUSTS COULD REACH THE
SURFACE. ADDITIONALLY, CANT RULE OUT THE POSSIBILITY OF A
WATERSPOUT IN THE MORNING, GIVEN DEEP-LAYER SHEAR OF AROUND 40 KTS
AND LOW-LEVEL SRH (STORM RELATIVE HELICITY) OF AROUND 150 M^2/S^2
COULD LEAD TO SOME STRONGER ROTATING UPDRAFTS.
SHORT TERM /SUNDAY NIGHT/
SUNDAY:
KEY POINTS
* SLIGHT RISK FOR SEVERE THUNDERSTORMS BETWEEN 2-10 PM.
* THE PRIMARY RISK IS STRONG TO DAMAGING WINDS WITH SMALL HAIL AND
HEAVY RAIN AS SECONDARY THREATS
SHOULD BEGIN TO SEE SOME CLEARING BEHIND THE MORNING CONVECTION WITH
SOME VERY SUBTLE HEIGHT RISING LEADING TO WEAK SUBSIDENCE. HIGH
TEMPERATURES WILL BE SIMILAR TO TODAY, REACHING THE LOW TO MID-80S,
BUT IT WILL FEEL WARMER AS DEWPOINTS NEAR 70°F WILL MAKE IT FEEL
LIKE THE UPPER 80S TO LOW 90S. THE INCREASED HEAT AND HUMIDITY WILL
ALLOW FOR INSTABILITY (MLCAPE), SUNDAY AFTERNOON REACHING BETWEEN
1000-1500 J/KG. AN APPROACHING COLD FRONT WILL THEN BECOME THE
FOCUS FOR STRONG TO SEVERE AFTERNOON/EVENING THUNDERSTORMS. WITH
DEEP LAYER SHEAR BETWEEN 30-40 KNOTS AND STRONG FORCING FROM THE
COLD FRONT, WE EXPECT THUNDERSTORMS TO QUICKLY ORGANIZE INTO LINEAR
CLUSTERS OF STORMS. THE PRIMARY THREAT IS STRONG TO DAMAGING WINDS
WITH ANY BOWING SEGMENTS WITH LOW-LEVEL LAPSE RATES BETWEEN 9- 11
°C/KM AND DCAPE VALUES NEAR 900 J/KG. HEAVY RAIN IS A CLOSE
SECONDARY THREAT IN THE AFTERNOON AS PWATS WILL BE AROUND 1.5
INCHES, BUT STORMS WILL LIKELY BE MOVING TOO FAST TO CAUSE ANY FLASH
FLOODING. SMALL HAIL IS POSSIBLE WITH STRONGER WINDS ALOFT, LEADING
TO ELONGATED HODOGRAPHS; HOWEVER, MID-LEVEL LAPSE RATES UNDER 6
°C/KM AND THE FREEZING LEVEL STILL AROUND 12 KFT MEAN HAIL ABOVE 1
INCH IS UNLIKELY. THE TORNADO THREAT IS VERY LOW TO NIL IN THE
AFTERNOON WITH AN UNFAVORABLE ENVIRONMENT FOR DISCRETE SUPERCELLS
AND MINIMAL LOW-LEVEL SHEAR AHEAD OF THE COLD FRONT.
HIGH-RESOLUTION GUIDANCE REMAINS IN GOOD AGREEMENT WITH THE TIMING
OF THE COLD FRONT AND THUNDERSTORMS. STORMS ARE LIKELY TO FORM NEAR
THE HIGH TERRAIN BETWEEN 2-5 P.M. AND MOVE SOUTHEAST IN A LINE OR
BOWING SEGMENT BETWEEN 5-10 P.M. STORMS WILL LIKELY BEGIN TO WEAKEN
AS THEY APPROACH THE MORE STABLE MARINE LAYER NEAR THE COASTS.
SUNDAY NIGHT:
DRYING TREND BEHIND THE COLD FRONT WITH NW WINDS ALLOWING DEWPOINTS
TO FALL BACK INTO THE UPPER 50S TO LOW 60S. PERHAPS NOT A PERFECT
RADIATIONAL COOLING NIGHT, EVEN WITH CLEAR SKIES, AS THE BOUNDARY
LAYER IS LIKELY TO REMAIN MIXED OUT WITH THE CAA. OVERNIGHT LOWS
DROP INTO THE UPPER 50S TO MID-60S.
LONG TERM /MONDAY THROUGH SATURDAY/
KEY MESSAGES...
* BEAUTIFUL MON/TUE WITH VERY COMFORTABLE HUMIDITY AND HIGHS MIDDLE
70S TO THE LOWER 80S AND LOWS IN THE 50S WITH SOME 40S MON NIGHT
* WARMING TREND BEGINS WED WITH 90+ HEAT & HUMIDITY RETURNING THU
AND ESPECIALLY BY FRI WHEN SOME LOCALES MAY REACH WELL INTO THE 90S
* MAIN RISK OF SHOWERS & T-STORMS SOMETIME FRI/FRI NIGHT WITH A COLD
FRONT...OTHERWISE EXPECT DRY WEATHER FOR MOST OF THE WEEK
DETAILS...
MONDAY AND TUESDAY...
A VERY PLEASANT POST-FRONTAL AIRMASS BEHIND SUNDAY/S COLD FRONT.
THIS WILL ALLOW FOR BELOW NORMAL TEMPS AND VERY COMFORTABLE HUMIDITY
LEVELS MON INTO TUE AS HIGH PRESSURE BUILDS SOUTH FROM QUEBEC. HIGH
TEMPS WILL BE IN THE MIDDLE 70S TO THE LOWER 80S WITH TUE BEING THE
COOLER DAY. RATHER COOL NIGHTS TOO WITH LOWS BOTTOMING OUT IN THE
50S...BUT SOME 40S ARE EXPECTED MON NIGHT IN THE OUTLYING LOCATIONS.
WEDNESDAY THROUGH SATURDAY...
HIGH PRESSURE MOVES EAST OF THE REGION BY WED AND THIS WILL BE THE
TRANSITION DAY. SOUTHWEST FLOW AND WARMING HEIGHT FIELDS WILL ALLOW
HIGHS WED TO RECOVER WELL INTO THE 80S. BY THU AND FRI...HEIGHT
FIELDS WILL CONTINUE TO RISE AND 850T WILL REACH OR EXCEED +20C.
THEREFORE...WE EXPECT HEAT AND HUMIDITY TO RETURN WITH 90+ HIGHS
RETURNING THU AND POSSIBLE SOME LOCALES WELL INTO THE 90S BY FRI.
THE AIRMASS WILL ALSO BECOME INCREASING MORE HUMID...SO WE CERTAINLY
MAY NEED ANOTHER ROUND OF HEAT ADVISORIES BY LATE NEXT WEEK.
AT THIS TIME...THE MAIN RISK FOR A ROUND OF SHOWERS & T-STORMS
APPEARS TO BE SOME TIME FRI/FRI NIGHT AS A COLD FRONT DROPS
SOUTHWARD ACROSS THE REGION. IT STILL MAY REMAIN QUITE WARM TO HOT
ON SAT AS THE MID LEVEL COOLING WILL BE LIMITED.
AVIATION /23Z SATURDAY THROUGH THURSDAY/
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MODERATE - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
00Z TAF UPDATE: HIGH CONFIDENCE.
VFR CONDITIONS CONTINUE THIS EVENING...THEN SOME MVFR WITH
LOCALIZED IFR CEILINGS DEVELOP AFTER 05Z/06Z THROUGH DAYBREAK
SUN. EXPECTING AN AREA OF SHOWERS AND EMBEDDED THUNDERSTORMS
WITH BRIEF DOWNPOURS NEAR SOUTH COAST AROUND DAYBREAK AND
SCATTERED SHOWERS ARE ALSO POSSIBLE FARTHER NORTH THROUGH 12-14Z
SUN. CEILINGS MAY LOWER TO IFR FOR A TIME SUN MORNING,
ESPECIALLY AROUND CAPE COD AND ISLANDS, OTHERWISE MVFR CEILINGS
SHOULD SCATTER OUT SUN AFTERNOON. FROM THERE, WE EXPECT A LINE
OF SCATTERED THUNDERSTORMS TO CROSS THE REGION FROM NW TO SE
LATER SUN AFTERNOON AND EVENING WITH POTENTIAL TO BRING IFR
CONDITIONS, STRONG WIND GUSTS, AND DOWNPOURS. TIMING IS ROUGHLY
20Z THROUGH 02Z, ALTHOUGH IT'S POSSIBLE THE LINE IS DELAYED BY A
FEW MORE HOURS. CLEARING FOLLOWS SUN NIGHT.
KBOS TERMINAL...HIGH CONFIDENCE IN TAF.
KBDL TERMINAL...HIGH CONFIDENCE IN TAF.
OUTLOOK /MONDAY THROUGH THURSDAY/...
MONDAY THROUGH MONDAY NIGHT: VFR. BREEZY.
TUESDAY THROUGH TUESDAY NIGHT: VFR.
WEDNESDAY THROUGH WEDNESDAY NIGHT: VFR. BREEZY.
THURSDAY: WINDY WITH LOCAL GUSTS UP TO 30 KT.
MARINE
FORECASTER CONFIDENCE LEVELS...
LOW - LESS THAN 30 PERCENT.
MEDIUM - 30 TO 60 PERCENT.
HIGH - GREATER THAN 60 PERCENT.
THROUGH SUNDAY NIGHT...HIGH CONFIDENCE.
INCREASING SOUTHERLY WINDS TONIGHT BETWEEN 15-20 KNOTS,
POSSIBLY GUSTING 25 KNOTS. CONFIDENCE WAS NOT HIGH ENOUGH TO
ISSUE A SCA. A ROUND OF STRONG TO POSSIBLY SEVERE THUNDERSTORMS
WILL AFFECT THE SOUTH COASTAL WATERS SUNDAY MORNING WITH A HIGH
CHANCE FOR SPECIAL MARINE WARNINGS BETWEEN 6AM-10AM. THESE
STORMS COULD PRODUCE GALE FORCE WINDS AND PERHAPS EVEN A
WATERSPOUT. CLEARING CONDITIONS BEHIND THE MORNING
THUNDERSTORMS. AFTERNOON THUNDERSTORMS FORM INLAND AND APPROACH
THE WATERS TOWARDS SUNSET. LOW CHANCE FOR SPECIAL MARINE
WARNINGS AS STORMS WILL LIKELY BE DISSIPATING AS THEY APPROACH
THE WATERS, BUT COULD STILL PRODUCE BRIEF GUSTY WINDS.
WINDS TURN NW BEHIND A COLD FRONT SUNDAY NIGHT AND GUST 20-25
KNOTS. NO SCAS AT THIS TIME, BUT MAY BE NEEDED IN THE FUTURE.
OUTLOOK /MONDAY THROUGH THURSDAY/...
MONDAY: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH GUSTS UP
TO 20 KT.
MONDAY NIGHT THROUGH WEDNESDAY: WINDS LESS THAN 25 KT.
WEDNESDAY NIGHT: LOW RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 25 KT.
THURSDAY: MODERATE RISK FOR SMALL CRAFT ADVISORY WINDS WITH
GUSTS UP TO 30 KT. AREAS OF SEAS APPROACHING 5 FT.
BOX WATCHES/WARNINGS/ADVISORIES
CT...NONE.
MA...NONE.
RI...NONE.
MARINE...NONE.
SYNOPSIS...KP/FRANK
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...FRANK
AVIATION...JWD/FRANK
MARINE...KP/FRANK
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